Resolution

Within 24 hours, the results of the diagnostic test analysis of Alex’s stool sample revealed that it was positive for
heat-labile enterotoxin (LT) ,
heat-stabile enterotoxin (ST) , and
colonization factor (CF) , confirming the hospital physician’s suspicion of
ETEC . During a follow-up with Alex’s family physician, this physician noted that Alex’s symptoms were not resolving quickly and he was experiencing discomfort that was preventing him from returning to classes. The family physician prescribed Alex a course of
ciprofloxacin to resolve his symptoms. Fortunately, the ciprofloxacin resolved Alex’s symptoms within a few days.

Alex likely got his infection from ingesting contaminated food or water. Emerging industrialized countries like Mexico are still developing sanitation practices that prevent the contamination of water with fecal material. Travelers in such countries should avoid the ingestion of undercooked foods, especially meats, seafood, vegetables, and unpasteurized dairy products. They should also avoid use of water that has not been treated; this includes drinking water, ice cubes, and even water used for brushing teeth. Using bottled water for these purposes is a good alternative. Good hygiene (handwashing) can also aid the prevention of an ETEC infection. Alex had not been careful about his food or water consumption, which led to his illness.

Alex’s symptoms were very similar to those of
cholera , caused by the gram-negative bacterium
Vibrio cholerae , which also produces a toxin similar to ST and LT. At some point in the evolutionary history of
ETEC , a nonpathogenic strain of
E. coli similar to those typically found in the gut may have acquired the genes encoding the ST and LT toxins from
V. cholerae . The fact that the genes encoding those toxins are encoded on extrachromosomal plasmids in ETEC supports the idea that these genes were acquired by
E. coli and are likely maintained in bacterial populations through horizontal gene transfer.

Viral genomes

Viral genomes exhibit significant diversity in structure. Some viruses have genomes that consist of DNA as their genetic material. This
DNA may be single stranded, as exemplified by human
parvoviruses , or double stranded, as seen in the
herpesviruses and
poxviruses . Additionally, although all cellular life uses DNA as its genetic material, some
viral genomes are made of either single-stranded or double-stranded RNA molecules, as we have discussed. Viral genomes are typically smaller than most bacterial genomes, encoding only a few genes, because they rely on their hosts to carry out many of the functions required for their
replication . The diversity of viral genome structures and their implications for viral replication life cycles are discussed in more detail in
The Viral Life Cycle .

Why do viral genomes vary widely among viruses?

Genome size matters

There is great variation in size of genomes among different organisms. Most eukaryotes maintain multiple chromosomes; humans, for example have 23 pairs, giving them 46 chromosomes. Despite being large at 3 billion base pairs, the human genome is far from the largest genome. Plants often maintain very large genomes, up to 150 billion base pairs, and commonly are polyploid, having multiple copies of each chromosome.

The size of
bacterial genomes also varies considerably, although they tend to be smaller than eukaryotic genomes (
[link] ). Some bacterial genomes may be as small as only 112,000 base pairs. Often, the size of a bacterium’s genome directly relates to how much the bacterium depends on its host for survival. When a bacterium relies on the host cell to carry out certain functions, it loses the genes encoding the abilities to carry out those functions itself. These types of bacterial endosymbionts are reminiscent of the prokaryotic origins of mitochondria and chloroplasts.

From a clinical perspective, obligate intracellular pathogens also tend to have small genomes (some around 1 million base pairs). Because host cells supply most of their nutrients, they tend to have a reduced number of genes encoding metabolic functions. Due to their small sizes, the genomes of organisms like
Mycoplasma genitalium (580,000 base pairs),
Chlamydia trachomatis (1.0 million),
Rickettsia prowazekii (1.1 million), and
Treponema pallidum (1.1 million) were some of the earlier bacterial genomes sequenced. Respectively, these pathogens cause urethritis and pelvic inflammation, chlamydia, typhus, and syphilis.

Whereas obligate intracellular pathogens have unusually small genomes, other bacteria with a great variety of metabolic and enzymatic capabilities have unusually large bacterial genomes.
Pseudomonas aeruginosa , for example, is a bacterium commonly found in the environment and is able to grow on a wide range of substrates. Its genome contains 6.3 million base pairs, giving it a high metabolic ability and the ability to produce virulence factors that cause several types of opportunistic infections
.

Interestingly, there has been significant variability in genome size in viruses as well, ranging from 3,500 base pairs to 2.5 million base pairs, significantly exceeding the size of many bacterial genomes. The great variation observed in viral genome sizes further contributes to the great diversity of viral genome characteristics already discussed.

There is great variability as well as overlap among the genome sizes of various groups of organisms and viruses.

Visit the
genome database of the National Center for Biotechnology Information (NCBI) to see the genomes that have been sequenced and their sizes.

Key concepts and summary

The entire genetic content of a cell is its
genome .

Genes code for proteins, or stable RNA molecules, each of which carries out a specific function in the cell.

Although the
genotype that a cell possesses remains constant, expression of genes is dependent on environmental conditions.

A
phenotype is the observable characteristics of a cell (or organism) at a given point in time and results from the complement of genes currently being used.

The majority of genetic material is organized into
chromosomes that contain the DNA that controls cellular activities.

Prokaryotes are typically haploid, usually having a single circular chromosome found in the nucleoid. Eukaryotes are diploid; DNA is organized into multiple linear chromosomes found in the nucleus.

Supercoiling and DNA packaging using DNA binding proteins allows lengthy molecules to fit inside a cell. Eukaryotes and archaea use histone proteins, and bacteria use different proteins with similar function.

Prokaryotic and eukaryotic genomes both contain
noncoding DNA , the function of which is not well understood. Some noncoding DNA appears to participate in the formation of small noncoding RNA molecules that influence gene expression; some appears to play a role in maintaining chromosomal structure and in DNA packaging.

Extrachromosomal DNA in eukaryotes includes the chromosomes found within organelles of prokaryotic origin (mitochondria and chloroplasts) that evolved by endosymbiosis. Some viruses may also maintain themselves extrachromosomally.

Extrachromosomal DNA in prokaryotes is commonly maintained as
plasmids that encode a few nonessential genes that may be helpful under specific conditions. Plasmids can be spread through a bacterial community by horizontal gene transfer.

Viral genomes show extensive variation and may be composed of either RNA or DNA, and may be either double or single stranded.

True/false

Within an organism, phenotypes may change while genotypes remain constant.

In the chromatin of eukaryotic cells, which regions of the chromosome would you expect to be more compact: the regions that contain genes being actively copied into RNA or those that contain inactive genes?

what is scale up fermenter ? and whict bectetia is benifited in industrial microbilogy ?

Nadiya

can u explain to me wts the meaning of autoclave,and how it doing and ,wt r the equipment to need to do it?

chandi

stem heat under pressure

Nadiya

thnks

chandi

autoclave is a steam heat under pressure .it is use to sterilize the equipment, agar ,petridish broth liquid and many more things....to kill the microbes.......free from microbes

Nadiya

nadiya
Scale up studies refers to the act of using results obtained from laboratory studies for designing a prototype and a pilot plant process. do you agree or

Norbuqaari

bectetia is benifited in industrial microbilogy is lactobacilli

Norbuqaari

and

Nadiya

chandi.
strong heated container used for chemical reactions and other processes using high pressures and temperatures, e.g. steam sterilization.

Norbuqaari

another

Norbuqaari

who is father of microbiology?

Norbuqaari

anton van leoven hook

chandi

antonie van leeuwenhoek

chandi

thanks

Norbuqaari

what is microbial taxonomy

Ini

what is normal flora

kifayat

normal flora contains the microorganisms which lives on and in our body but can not cause diseases easily....e.g staph. aureus lives on our body they dont cause disease in normal conditions whenever our skin is injured by any cut or wound then they enter into the body and cause diseases

Muhammad

two types of normal flora .... one is the resident normal flora and the other is transient normal flora.....resident normal flora is reside on our body in every condition but transient normal flora changes with the conditions

Muhammad

what is the method used for anaerobic bacteria to grow in the lab other then the candle jar method?

a member of a large group of unicellular microorganisms which have cell walls but lack organelles and on organised nucleus and ,including some which can cause disease

Nadiya

what is a germ

Ibrahim

a microorganisms,speciallay one which causes disease .

Nadiya

bacteria are a type of biological cells. They are unicellular. Bacteria were among the first life forms appear on the earth. they have a number of shapes, typically a few micrometers in length. They are present in of its habitata on earth.

isha

What is Auto clave?

Lovely

Autoclave is a pressure chamber used to sterilize equipments

praveen

hi

Lovely

n

vijaya

hii

chandi

what is a Laminar air flow?

isha

Laminar airflow cabinet is a carefully enclosed bench designed to prevent contamination of semiconductor wafers, biological samples or any particle sensitive materials

praveen

Praveen Deepi.... thnq....

isha

what bacteria causes malaria

Silas

female anaphilis mosquitos!

Nadiya

malaria isn`t caused by a bacteria rather by a digenetic parasite named Plasmodium.

lipids regulate membrane permeability,
lipids are storage compounds, triglycerides serve as reserve energy of the body,
lipids are the important compounds of cell membrane structure in eucaryotic cell,
lipids serve as source of fat soluble vitamins....

isha

what is dry heat

Shahid

C-reactiv proteins is a blood test marker inflammation in the body. It called CRP also. It's produced in the lever and it's level is measured by testing the blood. It is classified as an acute phase reachant, which mean that it's levels will rise in response to inflammation.

isha

what is stlization

Shahid

dry heat is used to kill the microorganisms.using of flame is an example for dry heat

SRUTHI

what is pasteurization

SRUTHI

what is mothed of dry heat

Shahid

the process of making something free from bacteria or other living microorganisms.

Nadiya

is called sterilization.

Nadiya

incineration

SRUTHI

buring

SRUTHI

incineration is a waste treatment process that involves the combustion of organic substance contain in waste material .this method also burns any organisms yo ash!

Nadiya

pasteurization is a process to kill or to finish the pathogenic microorganisms in milk or fruit juice (liquid food) by heat treatment... less than 100 degree Celsius....or 212 degree Fahrenheit temperature...

isha

pasteurization is a process of heating ,and then rapidly cooling ,liquid or food in order to kill microbes that may expedite their spoilage or cause disease .and .....French scientists who invented the process of pasteurization was Louis pasteur.

Nadiya

is the single celled organisms that can existance independent or dependent living